How to make the light emission invisible?
You can use a Light path node to mix shaders based on the properties of the incoming ray.

For example, this node setup mixes Base material and Line material based on Line texture, then mixes that with Base material based on the kind of incoming ray; rays coming directly from the camera will see the mix of Base and Line, but other rays will "see" only Base.



So shadows and indirect lighting etc. will be cast as if Base shader was connected straight to the material output.